Mongoose Update:
Commuting for 12 weeks now with the Mongoose electric bike from Walmart.
Averaging about 4 days per week of use so far, so about 50 trips.
Usually use full power going in to work with walking-effort pedalling.
Coming home probably half the time I just use pedal power, half the time full electric +more vigorous pedalling.
Probably this is draining the battery about 30% on a daily basis.
I did a timed run with no pedalling today to see how the battery was holding up.
Going in - 3.47mi, 12:58 minutes, avg speed 16.0 mph
Coming home - 3.88, 17:05, avg speed 13.6 mph, but about 2 minutes total wasted at stop lights and train crossing.
These figures are comparable to initial testing runs, so no definite change in performance at about 50 charges (from approx 30% drained level).